The presentation of an MPEG encoded video sequence in the reverse direction is a difficult problem considering that in an MPEG stream structure, a video access unit, corresponding to data representing one coded picture, may depend on previously transmitted pictures. Indeed, video access units are sent in an order which facilitates their decoding for display in forward direction. Thus, three reconstruction buffers are sufficient to decode the stream in this direction.
When playback in the reverse direction is required. be it at the normal rate or at an accelerated rate, one solution consists in decoding all pictures corresponding a group of pictures (generally 12 pictures) before displaying any picture from this group of pictures. The last picture (in forward direction display order) of such a group may indeed depend on the first picture of the group, which is an intra type picture. Only some of these decoded pictures may be displayed, depending on the playback speed.
Usual video decoders carry out one picture decoding per display period (e.g. 40 ms). This is not adapted to trickmode playback.